1. Field of the Invention
The present invention relates generally to the field of energy storage devices used to satisfy periods of peak demand for electricity. More specifically, the present invention discloses an energy storage device which creates a reservoir of compressed air by hydraulic air compression during periods of low demand of electricity, and then uses the compressed air to generate electricity during periods of peak demand.
2. Statement of the Problem
The demand for electricity faced by public utilities fluctuates on a seasonal basis and during the course of each day. Periods of peak demand for electricity typically occur during hot weather in the summer months, and in particular during late summer afternoons when air-conditioning loads are at a maximum. It is very expensive for an electrical utility to construct and maintain sufficient electrical generating capacity to meet such periods of peak demand. In recognition of this problem, public utilities have adopted a number of conservation strategies to help reduce peak electrical demands, such as load shedding and peak demand billing. On the supply side, utilities have created a network of interconnections to allow surplus electrical power to be bought and sold between utilities to help smooth out regional peak loads. However, the price of purchasing power during peak periods can be very high. Some utilities have constructed pumped storage facilities in which water is pumped into a reservoir during off-peak periods, and then used to generate hydro-electric power during peak periods. However, these facilities generally require construction of a dam to create the reservoir. Japan uses pumped storage to a greater degree than the United States. Forty five percent of Japan's hydroelectric power is by pumped storage, in comparison to less than one percent in the United States. Planning for peak demand became more difficult for the utility companies when the Public Utility Regulatory Policies Act of 1978 ("PURPA") became law. It insured non-utility power producers a market for their electricity by requiring the utilities to buy it at competitive rates. Since 1980, independent power producers have accounted for and will continue to furnish most of the replacement and growth needs of the industry.
The prior art contains several patents dealing with hydraulic air compression and use of air bubbles to create fluid movement, including the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Jensen 4,703,626 Nov. 3, 1987 Bervig 4,392,062 July 5, 1983 Santangelo, et al. 3,765,727 Oct. 16, 1973 Busick 4,135,364 Jan. 23, 1979 Angle 4,278,405 July 14, 1981 Girden 4,355,513 Oct. 26, 1982 ______________________________________
The inventor's previous patent, U.S. Pat. No. 4,703,626 discloses an energy conversion apparatus used to generate electricity using ocean thermal gradients and salinity gradients. Air bubbles are introduced into the flow of warm, high-salinity sea water downward at the upper opening of the apparatus. This air is subject to hydraulic compression as the water falls. The flow of sea water and air drives a turbine to produce electricity, and then passes through a cooling tube near the bottom of the apparatus where it is cooled to the ambient ocean temperature at that depth. The flow then enters a chamber where the air and water are allowed to separate. Because of its greater density than the ambient sea water at that depth, the water in the chamber tends to flow out exhaust ports located at the bottom of the separation chamber.
Bervig discloses an energy storage and generation device in which air is compressed, by means of a conventional air compressor, and stored in a large tank during off-peak periods. During periods of peak power demand, compressed air from the tank is released to create bubbles in one leg of a U-shaped conduit filled with fluid. The resulting circulation of fluid within the conduit is used to drive a generator to produce power.
Santangelo, et al., disclose an apparatus for transporting mined deposits, such as manganese nodules, from the sea floor by injecting air into a dredge pipe at a location somewhat below the surface of the water. The air bubbles cause an upward flow of water and accompanying mined materials from the bottom opening of the dredge pipe to the ocean surface.
Busick discloses an apparatus in which air bubbles are introduced into a number of vertical tubes immersed in water. The resulting upward flow of water is used to drive a turbine-like fluid motor.
Angle discloses an apparatus for producing compressed air by entraining air in a downward flow of water. A separating cone and chamber are used to separate the air from the water at the bottom of the apparatus.
Girden discloses an apparatus for generating power by bubbling air through vertical tubes immersed in the ocean. The air bubbles cause an upward flow of cool sea water through the tubes. This creates a region of cool air above the ocean which creates winds used to drive windmills to produce power.
3. Solution to the Problem
None of the prior art references uncovered in the search show the specific structure of the present invention. In particular, none of the prior art references use hydraulic air compression to create a reservoir of compressed air during off-peak periods, that is used to create air bubbles to induce a flow of water to drive a turbine and thereby generate power during periods of peak demand for electricity.